There’s been a lot of previous interest in indoor CO2 in the rationality community, including an (unsuccessful) CO2 stripper project, some researchsummaries and self experiments. The results are confusing, I suspect some of the older research might be fake. But I noticed something that has greatly changed how I think about CO2 in relation to cognition.
Exhaled air is about 50kPPM CO2. Outdoor air is about 400ppm; indoor air ranges from 500 to 1500ppm depending on ventilation. Since exhaled air has CO2 about two orders of magnitude larger than the variance in room CO2, if even a small percentage of inhaled air is reinhalation of exhaled air, this will have a significantly larger effect than changes in ventilation. I’m having trouble finding a straight answer about what percentage of inhaled air is rebreathed (other than in the context of mask-wearing), but given the diffusivity of CO2, I would be surprised if it wasn’t at least 1%.
This predicts that a slight breeze, which replaces their in front of your face and prevents reinhalation, would have a considerably larger effect than ventilating an indoor space where the air is mostly still. This matches my subjective experience of indoor vs outdoor spaces, which, while extremely confounded, feels like an air-quality difference larger than CO2 sensors would predict.
This also predicts that a small fan, positioned so it replaces the air in front of my face, would have a large effect on the same axis as improved ventilation would. I just set one up. I don’t know whether it’s making a difference but I plan to leave it there for at least a few days.
(Note: CO2 is sometimes used as a proxy for ventilation in contexts where the thing you actually care about is respiratory aerosol, because it affects transmissibility of respiratory diseases like COVID and influenza. This doesn’t help with that at all and if anything would make it worse.)
This indicates that how we breathe plays a big role in CO2 uptake. Like, shallow or full, small or large volumes, or the speed of exhaling. Breathing technique is a key skill of divers and can be learned. I just started reading the book Breath, which seems to have a lot on it.
Huh, I’ve also noticed a larger effect from indoors/outdoors than seems reflected by CO2 monitors, and that I seem smarter when it’s windy, but I never thought of this hypothesis; it’s interesting, thanks.
I assume the 44k PPM CO2 exhaled air is the product of respiration (I.e. the lungs have processed it), whereas the air used in mouth-to-mouth is quickly inhaled and exhaled.
As the respirator still has to breathe regularly, there will be still a significantly higher CO2 in the air for respiration. I’d guess maybe half − 20k PPM. Interesting to see somebody measure that.
I had previously guessed air movement made me feel better because my body expected air movement (i.e. some kind of biophilic effect). But this explanation seems more likely in retrospect! I’m not quite sure how to run the calculation using the diffusivity coefficient to spot check this, though.
There’s been a lot of previous interest in indoor CO2 in the rationality community, including an (unsuccessful) CO2 stripper project, some research summaries and self experiments. The results are confusing, I suspect some of the older research might be fake. But I noticed something that has greatly changed how I think about CO2 in relation to cognition.
Exhaled air is about 50kPPM CO2. Outdoor air is about 400ppm; indoor air ranges from 500 to 1500ppm depending on ventilation. Since exhaled air has CO2 about two orders of magnitude larger than the variance in room CO2, if even a small percentage of inhaled air is reinhalation of exhaled air, this will have a significantly larger effect than changes in ventilation. I’m having trouble finding a straight answer about what percentage of inhaled air is rebreathed (other than in the context of mask-wearing), but given the diffusivity of CO2, I would be surprised if it wasn’t at least 1%.
This predicts that a slight breeze, which replaces their in front of your face and prevents reinhalation, would have a considerably larger effect than ventilating an indoor space where the air is mostly still. This matches my subjective experience of indoor vs outdoor spaces, which, while extremely confounded, feels like an air-quality difference larger than CO2 sensors would predict.
This also predicts that a small fan, positioned so it replaces the air in front of my face, would have a large effect on the same axis as improved ventilation would. I just set one up. I don’t know whether it’s making a difference but I plan to leave it there for at least a few days.
(Note: CO2 is sometimes used as a proxy for ventilation in contexts where the thing you actually care about is respiratory aerosol, because it affects transmissibility of respiratory diseases like COVID and influenza. This doesn’t help with that at all and if anything would make it worse.)
This indicates that how we breathe plays a big role in CO2 uptake. Like, shallow or full, small or large volumes, or the speed of exhaling. Breathing technique is a key skill of divers and can be learned. I just started reading the book Breath, which seems to have a lot on it.
Huh, I’ve also noticed a larger effect from indoors/outdoors than seems reflected by CO2 monitors, and that I seem smarter when it’s windy, but I never thought of this hypothesis; it’s interesting, thanks.
Ah, very related: Exhaled air contains 44000 PPM CO2 and is used for Mouth-to-mouth resuscitation without problems.
I assume the 44k PPM CO2 exhaled air is the product of respiration (I.e. the lungs have processed it), whereas the air used in mouth-to-mouth is quickly inhaled and exhaled.
As the respirator still has to breathe regularly, there will be still a significantly higher CO2 in the air for respiration. I’d guess maybe half − 20k PPM. Interesting to see somebody measure that.
How did this experiment go?
I had previously guessed air movement made me feel better because my body expected air movement (i.e. some kind of biophilic effect). But this explanation seems more likely in retrospect! I’m not quite sure how to run the calculation using the diffusivity coefficient to spot check this, though.
That’s a really neat point, has it ever been addressed in prior literature, that you’ve gone over?